1. Field of the Invention
The present invention relates to temperature controlled heated molds for thermoplastic materials and, more particularly, to radio frequency heated molds for forming, molding, welding or extruding thermoplastic materials and circuits therefor.
2. Background of the Invention
In the field of catheters formed of flexible plastic tubing and used in angioplasty and other procedures, the tips and assembly joints have to be smoothed to enhance medical procedures and to minimize a likelihood of injury to human tissue. Such smoothing has been accomplished by mechanical or chemical milling or reforming the tips. Alternatively, application of heat from an open flame or other heat source has been used to slightly melt and thereby re-contour the tips. To attach two lengths of tubing end to end, chemical bonding is often used. Alternatively, a source of heat may be applied to the junction of thermoplastic tubing to cause melting and welding of the ends of the tubing; typically, such a junction has discontinuities on the interior and the exterior surfaces. Annular attachment of one length of tubing with a cylindrical segment is usually performed through chemical welding or bonding because of difficulties associated in application of a controlled amount of heat to effect welding. Similarly, balloons of the type used in angioplasty procedures are usually chemically welded to a length of tubing having one or more lumen.
While a weld formed chemically usually meets the requisite structural criteria, various problems are associated therewith. In particular, residue of the chemical must be removed. When such chemical is present interior of tubing, extra care in removing it must be taken. The chemical welding process does not always provide smooth weld joints. Furthermore, during assembly the chemicals are usually toxic and create health hazards to production workers. When any of various conventional heat sources are used to effect welding, control of the heat applied is generally difficult. The lack of precise control of temperature of the location of the temperature of the heat applied may result in weak or partial welds. Alternatively, thin or weak spots may develop due to flow of thermoplastic material if too much heat is applied.
Whether prior art processes employ chemicals or conventional heat sources, several problems are present. First, a substantial amount of time must be expended by a technician to form, bond or weld the thermoplastic material. Second, such time expenditure creates a substantial increase in cost of manufacture. Third, integrity of the procedure is not always assured with potential hazardous consequences during an angioplasty procedure. Fourth, such questionable integrity mandates extensive quality control procedures which are expensive and result in poor manufacturing needs. Fifth, lack of consistent uniformity renders each product unique and therefore not commensurate with the consistent quality of large scale production and use requirements of medical products.